Cache Flushes and Content Updates Ignored on other Memached Instances

We have to two load balanced web servers, each running an instance of memcached; both web servers connect to a single MySQL server. We are seeing this behavior when publishing content and clearing caches:

* Publishing Content from server1: When content is updated and published on server1, it does not appear on server2. I have to execute a "Flush All Caches" > "Cache Tables" *on server2* for updates to appear on server2. The same also happens in reverse -- when content is published from server2.

Expected behavior would be that updating content on one server, reflects on all other servers.

* Running "Flush All Caches" or "Flush All Caches" > "Cache Tables" on server 1 flushes cache on server1, but not on server2 and vice versa.

Expected behavior would be that "Flush All Caches" on *one* server, flushes cache on *all* other servers defined in settings.php.

My settings.php around memcached is as follows:

  include_once('./includes/cache.inc');
  include_once('./sites/all/modules/contrib/memcache/memcache.inc');
  $conf['cache_default_class'] = 'MemCacheDrupal';
  $conf['memcache_servers'] = array(
      '11.22.33.44:11211' => 'default',
      '11.22.33.45:11211' => 'default',
    );
  $conf['memcache_bins'] = array('cache' => 'default');
  $conf['memcache_options'] = array(
   Memcached::OPT_COMPRESSION => TRUE,
   Memcached::OPT_BINARY_PROTOCOL => TRUE,
  );
  $conf['memcache_persistent'] = TRUE;
  $conf['memcache_key_prefix'] = $_SERVER['SERVER_NAME'];

Other interesting things of note:

* when I run drush vget memcache_servers, I get a No matching variable found., but I see hits to the memcache server.
* http://host/admin/reports/memcache -- shows stats for "localhost:11211" instead of showing stats for both servers defined in settings.php.
* Drupal 7.9, memcached version : 1.4.10; memcached php extension: 1.0.0.

Anyone else seeing this? How might one go about resolving this?