If I `curl` Phabricator with the `Host` header set to some non-existent domain, then I get an Internal Server Error:
```lang=bash
> curl -I https://phabricator.example.com -H 'Host: foobar.com'
curl: (22) The requested URL returned error: 500 Internal Server Error
```
The error in the PHP logs:
```
[11-Aug-2014 03:12:35 UTC] [Core Exception/Exception] Specified domain foobar.com is not configured for Phabricator requests. Please use https://phabricator.example.com to visit this instance.
#0 /usr/src/phabricator/webroot/index.php(70): AphrontApplicationConfiguration->buildController()
#1 {main}
[11-Aug-2014 03:12:35 UTC] PHP Fatal error: Uncaught exception 'Exception' with message 'AphrontWriteGuard was not properly disposed of! Call dispose() on every AphrontWriteGuard object you instantiate or use phutil_exit() to exit abruptly while debugging.' in /usr/src/libphutil/src/aphront/writeguard/AphrontWriteGuard.php:280
Stack trace:
#0 [internal function]: AphrontWriteGuard->__destruct()
#1 {main}
thrown in /usr/src/libphutil/src/aphront/writeguard/AphrontWriteGuard.php on line 280
```
I don't think that a 500 is the appropriate HTTP response ehre.