diff --git a/src/__phutil_library_map__.php b/src/__phutil_library_map__.php
--- a/src/__phutil_library_map__.php
+++ b/src/__phutil_library_map__.php
@@ -22,6 +22,7 @@
     'AlmanacBindingTransactionQuery' => 'applications/almanac/query/AlmanacBindingTransactionQuery.php',
     'AlmanacBindingViewController' => 'applications/almanac/controller/AlmanacBindingViewController.php',
     'AlmanacBindingsSearchEngineAttachment' => 'applications/almanac/engineextension/AlmanacBindingsSearchEngineAttachment.php',
+    'AlmanacCacheEngineExtension' => 'applications/almanac/engineextension/AlmanacCacheEngineExtension.php',
     'AlmanacClusterDatabaseServiceType' => 'applications/almanac/servicetype/AlmanacClusterDatabaseServiceType.php',
     'AlmanacClusterRepositoryServiceType' => 'applications/almanac/servicetype/AlmanacClusterRepositoryServiceType.php',
     'AlmanacClusterServiceType' => 'applications/almanac/servicetype/AlmanacClusterServiceType.php',
@@ -584,6 +585,7 @@
     'DiffusionBrowseQueryConduitAPIMethod' => 'applications/diffusion/conduit/DiffusionBrowseQueryConduitAPIMethod.php',
     'DiffusionBrowseResultSet' => 'applications/diffusion/data/DiffusionBrowseResultSet.php',
     'DiffusionBrowseTableView' => 'applications/diffusion/view/DiffusionBrowseTableView.php',
+    'DiffusionCacheEngineExtension' => 'applications/diffusion/engineextension/DiffusionCacheEngineExtension.php',
     'DiffusionCachedResolveRefsQuery' => 'applications/diffusion/query/DiffusionCachedResolveRefsQuery.php',
     'DiffusionChangeController' => 'applications/diffusion/controller/DiffusionChangeController.php',
     'DiffusionChangeHeraldFieldGroup' => 'applications/diffusion/herald/DiffusionChangeHeraldFieldGroup.php',
@@ -2023,6 +2025,8 @@
     'PhabricatorBulkContentSource' => 'infrastructure/daemon/contentsource/PhabricatorBulkContentSource.php',
     'PhabricatorBusyUIExample' => 'applications/uiexample/examples/PhabricatorBusyUIExample.php',
     'PhabricatorCacheDAO' => 'applications/cache/storage/PhabricatorCacheDAO.php',
+    'PhabricatorCacheEngine' => 'applications/system/engine/PhabricatorCacheEngine.php',
+    'PhabricatorCacheEngineExtension' => 'applications/system/engine/PhabricatorCacheEngineExtension.php',
     'PhabricatorCacheGeneralGarbageCollector' => 'applications/cache/garbagecollector/PhabricatorCacheGeneralGarbageCollector.php',
     'PhabricatorCacheManagementPurgeWorkflow' => 'applications/cache/management/PhabricatorCacheManagementPurgeWorkflow.php',
     'PhabricatorCacheManagementWorkflow' => 'applications/cache/management/PhabricatorCacheManagementWorkflow.php',
@@ -4571,6 +4575,7 @@
     'AlmanacBindingTransactionQuery' => 'PhabricatorApplicationTransactionQuery',
     'AlmanacBindingViewController' => 'AlmanacServiceController',
     'AlmanacBindingsSearchEngineAttachment' => 'AlmanacSearchEngineAttachment',
+    'AlmanacCacheEngineExtension' => 'PhabricatorCacheEngineExtension',
     'AlmanacClusterDatabaseServiceType' => 'AlmanacClusterServiceType',
     'AlmanacClusterRepositoryServiceType' => 'AlmanacClusterServiceType',
     'AlmanacClusterServiceType' => 'AlmanacServiceType',
@@ -5225,6 +5230,7 @@
     'DiffusionBrowseQueryConduitAPIMethod' => 'DiffusionQueryConduitAPIMethod',
     'DiffusionBrowseResultSet' => 'Phobject',
     'DiffusionBrowseTableView' => 'DiffusionView',
+    'DiffusionCacheEngineExtension' => 'PhabricatorCacheEngineExtension',
     'DiffusionCachedResolveRefsQuery' => 'DiffusionLowLevelQuery',
     'DiffusionChangeController' => 'DiffusionController',
     'DiffusionChangeHeraldFieldGroup' => 'HeraldFieldGroup',
@@ -6883,6 +6889,8 @@
     'PhabricatorBulkContentSource' => 'PhabricatorContentSource',
     'PhabricatorBusyUIExample' => 'PhabricatorUIExample',
     'PhabricatorCacheDAO' => 'PhabricatorLiskDAO',
+    'PhabricatorCacheEngine' => 'Phobject',
+    'PhabricatorCacheEngineExtension' => 'Phobject',
     'PhabricatorCacheGeneralGarbageCollector' => 'PhabricatorGarbageCollector',
     'PhabricatorCacheManagementPurgeWorkflow' => 'PhabricatorCacheManagementWorkflow',
     'PhabricatorCacheManagementWorkflow' => 'PhabricatorManagementWorkflow',
diff --git a/src/applications/almanac/engineextension/AlmanacCacheEngineExtension.php b/src/applications/almanac/engineextension/AlmanacCacheEngineExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/almanac/engineextension/AlmanacCacheEngineExtension.php
@@ -0,0 +1,53 @@
+<?php
+
+final class AlmanacCacheEngineExtension
+  extends PhabricatorCacheEngineExtension {
+
+  const EXTENSIONKEY = 'almanac';
+
+  public function getExtensionName() {
+    return pht('Almanac Core Objects');
+  }
+
+  public function discoverLinkedObjects(
+    PhabricatorCacheEngine $engine,
+    array $objects) {
+    $viewer = $engine->getViewer();
+
+    $results = array();
+    foreach ($this->selectObjects($objects, 'AlmanacBinding') as $object) {
+      $results[] = $object->getServicePHID();
+      $results[] = $object->getDevicePHID();
+      $results[] = $object->getInterfacePHID();
+    }
+
+    $devices = $this->selectObjects($objects, 'AlmanacDevice');
+    if ($devices) {
+      $interfaces = id(new AlmanacInterfaceQuery())
+        ->setViewer($viewer)
+        ->withDevicePHIDs(mpull($devices, 'getPHID'))
+        ->execute();
+      foreach ($interfaces as $interface) {
+        $results[] = $interface;
+      }
+    }
+
+    foreach ($this->selectObjects($objects, 'AlmanacInterface') as $iface) {
+      $results[] = $iface->getDevicePHID();
+      $results[] = $iface->getNetworkPHID();
+    }
+
+    foreach ($this->selectObjects($objects, 'AlmanacProperty') as $object) {
+      $results[] = $object->getObjectPHID();
+    }
+
+    return $results;
+  }
+
+  public function deleteCaches(
+    PhabricatorCacheEngine $engine,
+    array $objects) {
+    return;
+  }
+
+}
diff --git a/src/applications/diffusion/engineextension/DiffusionCacheEngineExtension.php b/src/applications/diffusion/engineextension/DiffusionCacheEngineExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/diffusion/engineextension/DiffusionCacheEngineExtension.php
@@ -0,0 +1,52 @@
+<?php
+
+final class DiffusionCacheEngineExtension
+  extends PhabricatorCacheEngineExtension {
+
+  const EXTENSIONKEY = 'diffusion';
+
+  public function getExtensionName() {
+    return pht('Diffusion Repositories');
+  }
+
+  public function discoverLinkedObjects(
+    PhabricatorCacheEngine $engine,
+    array $objects) {
+    $viewer = $engine->getViewer();
+    $results = array();
+
+    // When an Almanac Service changes, update linked repositories.
+
+    $services = $this->selectObjects($objects, 'AlmanacService');
+    if ($services) {
+      $repositories = id(new PhabricatorRepositoryQuery())
+        ->setViewer($viewer)
+        ->withAlmanacServicePHIDs(mpull($services, 'getPHID'))
+        ->execute();
+      foreach ($repositories as $repository) {
+        $results[] = $repository;
+      }
+    }
+
+    return $results;
+  }
+
+  public function deleteCaches(
+    PhabricatorCacheEngine $engine,
+    array $objects) {
+
+    $keys = array();
+    $repositories = $this->selectObjects($objects, 'PhabricatorRepository');
+    foreach ($repositories as $repository) {
+      $keys[] = $repository->getAlmanacServiceCacheKey();
+    }
+
+    $keys = array_filter($keys);
+
+    if ($keys) {
+      $cache = PhabricatorCaches::getMutableStructureCache();
+      $cache->deleteKeys($keys);
+    }
+  }
+
+}
diff --git a/src/applications/repository/query/PhabricatorRepositoryQuery.php b/src/applications/repository/query/PhabricatorRepositoryQuery.php
--- a/src/applications/repository/query/PhabricatorRepositoryQuery.php
+++ b/src/applications/repository/query/PhabricatorRepositoryQuery.php
@@ -12,6 +12,7 @@
   private $uris;
   private $datasourceQuery;
   private $slugs;
+  private $almanacServicePHIDs;
 
   private $numericIdentifiers;
   private $callsignIdentifiers;
@@ -134,6 +135,11 @@
     return $this;
   }
 
+  public function withAlmanacServicePHIDs(array $phids) {
+    $this->almanacServicePHIDs = $phids;
+    return $this;
+  }
+
   public function needCommitCounts($need_counts) {
     $this->needCommitCounts = $need_counts;
     return $this;
@@ -659,6 +665,13 @@
         $try_uris);
     }
 
+    if ($this->almanacServicePHIDs !== null) {
+      $where[] = qsprintf(
+        $conn,
+        'r.almanacServicePHID IN (%Ls)',
+        $this->almanacServicePHIDs);
+    }
+
     return $where;
   }
 
diff --git a/src/applications/repository/storage/PhabricatorRepository.php b/src/applications/repository/storage/PhabricatorRepository.php
--- a/src/applications/repository/storage/PhabricatorRepository.php
+++ b/src/applications/repository/storage/PhabricatorRepository.php
@@ -1865,21 +1865,25 @@
     $never_proxy,
     array $protocols) {
 
-    $service = $this->loadAlmanacService();
-    if (!$service) {
+    $cache_key = $this->getAlmanacServiceCacheKey();
+    if (!$cache_key) {
       return null;
     }
 
-    $bindings = $service->getActiveBindings();
-    if (!$bindings) {
-      throw new Exception(
-        pht(
-          'The Almanac service for this repository is not bound to any '.
-          'interfaces.'));
+    $cache = PhabricatorCaches::getMutableStructureCache();
+    $uris = $cache->getKey($cache_key, false);
+
+    // If we haven't built the cache yet, build it now.
+    if ($uris === false) {
+      $uris = $this->buildAlmanacServiceURIs();
+      $cache->setKey($cache_key, $uris);
     }
 
-    $local_device = AlmanacKeys::getDeviceID();
+    if ($uris === null) {
+      return null;
+    }
 
+    $local_device = AlmanacKeys::getDeviceID();
     if ($never_proxy && !$local_device) {
       throw new Exception(
         pht(
@@ -1890,10 +1894,8 @@
 
     $protocol_map = array_fuse($protocols);
 
-    $uris = array();
-    foreach ($bindings as $binding) {
-      $iface = $binding->getInterface();
-
+    $results = array();
+    foreach ($uris as $uri) {
       // If we're never proxying this and it's locally satisfiable, return
       // `null` to tell the caller to handle it locally. If we're allowed to
       // proxy, we skip this check and may proxy the request to ourselves.
@@ -1901,22 +1903,17 @@
       // return `null`, and then the request will actually run.)
 
       if ($local_device && $never_proxy) {
-        if ($iface->getDevice()->getName() == $local_device) {
+        if ($uri['device'] == $local_device) {
           return null;
         }
       }
 
-      $uri = $this->getClusterRepositoryURIFromBinding($binding);
-
-      $protocol = $uri->getProtocol();
-      if (empty($protocol_map[$protocol])) {
-        continue;
+      if (isset($protocol_map[$uri['protocol']])) {
+        $results[] = new PhutilURI($uri['uri']);
       }
-
-      $uris[] = $uri;
     }
 
-    if (!$uris) {
+    if (!$results) {
       throw new Exception(
         pht(
           'The Almanac service for this repository is not bound to any '.
@@ -1931,10 +1928,51 @@
           'Cluster hosts must correctly route their intracluster requests.'));
     }
 
-    shuffle($uris);
-    return head($uris);
+    shuffle($results);
+    return head($results);
   }
 
+  public function getAlmanacServiceCacheKey() {
+    $service_phid = $this->getAlmanacServicePHID();
+    if (!$service_phid) {
+      return null;
+    }
+
+    $repository_phid = $this->getPHID();
+    return "diffusion.repository({$repository_phid}).service({$service_phid})";
+  }
+
+  private function buildAlmanacServiceURIs() {
+    $service = $this->loadAlmanacService();
+    if (!$service) {
+      return null;
+    }
+
+    $bindings = $service->getActiveBindings();
+    if (!$bindings) {
+      throw new Exception(
+        pht(
+          'The Almanac service for this repository is not bound to any '.
+          'interfaces.'));
+    }
+
+    $uris = array();
+    foreach ($bindings as $binding) {
+      $iface = $binding->getInterface();
+
+      $uri = $this->getClusterRepositoryURIFromBinding($binding);
+      $protocol = $uri->getProtocol();
+      $device_name = $iface->getDevice()->getName();
+
+      $uris[] = array(
+        'protocol' => $protocol,
+        'uri' => (string)$uri,
+        'device' => $device_name,
+      );
+    }
+
+    return $uris;
+  }
 
   /**
    * Build a new Conduit client in order to make a service call to this
diff --git a/src/applications/system/engine/PhabricatorCacheEngine.php b/src/applications/system/engine/PhabricatorCacheEngine.php
new file mode 100644
--- /dev/null
+++ b/src/applications/system/engine/PhabricatorCacheEngine.php
@@ -0,0 +1,94 @@
+<?php
+
+final class PhabricatorCacheEngine extends Phobject {
+
+  public function getViewer() {
+    return PhabricatorUser::getOmnipotentUser();
+  }
+
+  public function updateObject($object) {
+    $objects = array(
+      $object->getPHID() => $object,
+    );
+
+    $new_objects = $objects;
+    while (true) {
+      $discovered_objects = array();
+      $load = array();
+
+      $extensions = PhabricatorCacheEngineExtension::getAllExtensions();
+      foreach ($extensions as $key => $extension) {
+        $discoveries = $extension->discoverLinkedObjects($this, $new_objects);
+        if (!is_array($discoveries)) {
+          throw new Exception(
+            pht(
+              'Cache engine extension "%s" did not return a list of linked '.
+              'objects.',
+              get_class($extension)));
+        }
+
+        foreach ($discoveries as $discovery) {
+          if ($discovery === null) {
+            // This is allowed because it makes writing extensions a lot
+            // easier if they don't have to check that related PHIDs are
+            // actually set to something.
+            continue;
+          }
+
+          $is_phid = is_string($discovery);
+          if ($is_phid) {
+            $phid = $discovery;
+          } else {
+            $phid = $discovery->getPHID();
+            if (!$phid) {
+              throw new Exception(
+                pht(
+                  'Cache engine extension "%s" returned object (of class '.
+                  '"%s") with no PHID.',
+                  get_class($extension),
+                  get_class($discovery)));
+            }
+          }
+
+          if (isset($objects[$phid])) {
+            continue;
+          }
+
+          if ($is_phid) {
+            $load[$phid] = $phid;
+          } else {
+            $objects[$phid] = $discovery;
+            $discovered_objects[$phid] = $discovery;
+
+            // If another extension only knew about the PHID of this object,
+            // we don't need to load it any more.
+            unset($load[$phid]);
+          }
+        }
+      }
+
+      if ($load) {
+        $load_objects = id(new PhabricatorObjectQuery())
+          ->setViewer($this->getViewer())
+          ->withPHIDs($load)
+          ->execute();
+        foreach ($load_objects as $phid => $loaded_object) {
+          $objects[$phid] = $loaded_object;
+          $discovered_objects[$phid] = $loaded_object;
+        }
+      }
+
+      // If we didn't find anything new to update, we're all set.
+      if (!$discovered_objects) {
+        break;
+      }
+
+      $new_objects = $discovered_objects;
+    }
+
+    foreach ($extensions as $extension) {
+      $extension->deleteCaches($this, $objects);
+    }
+  }
+
+}
diff --git a/src/applications/system/engine/PhabricatorCacheEngineExtension.php b/src/applications/system/engine/PhabricatorCacheEngineExtension.php
new file mode 100644
--- /dev/null
+++ b/src/applications/system/engine/PhabricatorCacheEngineExtension.php
@@ -0,0 +1,42 @@
+<?php
+
+abstract class PhabricatorCacheEngineExtension extends Phobject {
+
+  final public function getExtensionKey() {
+    return $this->getPhobjectClassConstant('EXTENSIONKEY');
+  }
+
+  abstract public function getExtensionName();
+
+  public function discoverLinkedObjects(
+    PhabricatorCacheEngine $engine,
+    array $objects) {
+    return array();
+  }
+
+  public function deleteCaches(
+    PhabricatorCacheEngine $engine,
+    array $objects) {
+    return null;
+  }
+
+  final public static function getAllExtensions() {
+    return id(new PhutilClassMapQuery())
+      ->setAncestorClass(__CLASS__)
+      ->setUniqueMethod('getExtensionKey')
+      ->execute();
+  }
+
+  final public function selectObjects(array $objects, $class_name) {
+    $results = array();
+
+    foreach ($objects as $phid => $object) {
+      if ($object instanceof $class_name) {
+        $results[$phid] = $object;
+      }
+    }
+
+    return $results;
+  }
+
+}
diff --git a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
--- a/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
+++ b/src/applications/transactions/editor/PhabricatorApplicationTransactionEditor.php
@@ -987,6 +987,10 @@
       throw $ex;
     }
 
+    // If we need to perform cache engine updates, execute them now.
+    id(new PhabricatorCacheEngine())
+      ->updateObject($object);
+
     // Now that we've completely applied the core transaction set, try to apply
     // Herald rules. Herald rules are allowed to either take direct actions on
     // the database (like writing flags), or take indirect actions (like saving