I use this code
Above answer by Piskvor did it for me. Its crazy how many hours I've spend trying to figure this out.
Main problem with plugins such as this Facebook for CakePHP is that they don't come with updates. APIs, especially popular ones like Facebook, change all the time because they are being imporved. If the guy who wrote it initially as a hobby moves on with his life and stops updating the SDK people who are less knowladgable on how to alter these things become stuck.
WORKING CODE:
Nevertheless, thanks for a great solution Piskvor, here is my piece of code for
apps/plugins/facebook/views/helpers/facebook.php
$init .= $this->Html->scriptBlock(
<<
The key piece of code here is:
FB.Event.subscribe("auth.logout", function() {
window.location = '/users/logout'
});
{$callback}