Logout / Force recheck

The FB authentication is done successfully but then even after the user logs out from facebook itself, he is still taken for granted in my website staying logged in. What is the necessary procedure to allow him to be logged out?

I think I managed to achieve the effect by unsetting $GLOBALS[_SESSION][OAUTH_STATE] & $GLOBALS[_SESSION][OAUTH_ACCESS_TOKEN]

e.g.,
if($_GET[logout])
{
unset($GLOBALS[_SESSION][OAUTH_STATE]);
unset($GLOBALS[_SESSION][OAUTH_ACCESS_TOKEN]);
}

This way, if the user has logged out from Facebook, he is asked to re-login; if he's still logged in to facebook, no effect as the check via the graph succeeds.

and the most radical way:
$_COOKIE = Array();
$_SESSION = Array();

The user being logged in has nothing to do with OAuth tokens. These are often used to access the API when the user is not present.

What you can do is to call ResetAccessToken function so the class cleans the stored tokens, although they are still valid until they expire.