How to setup Page Cache to work with the Flag Module and Views?
Similar to the first answer but not assuming your cache is in the database. (memcache, redis, apc, etc)

function hook_flag_flag($flag, $entity_id, $account, $flagging) {
  $view_name = '&lt;view_name&gt;';
  $display_id = '&lt;display_id&gt;';
  $cid = $view_name . ':' . $display_id . ':*';
  cache_clear_all($cid, $bin = 'cache_views_data', $wildcard = TRUE);
}