discovering if the user has logged out of facebook or not using facebooker2

I'm using facebooker2 with my site unfortunately even if i logged out of facebook.com my site:

1. fb_cookie still contains stuff eg:

access_token=xxxxx&base_domain=mysite.com&expires=1319101200&secret=yyyyyyyyy&sig=zzzzzzz&uid=1234567890 it never gets invalidated

1. current_facebook_user still contains the current facebook user.

How do i:

1. invalidate those variables
2. know if the user has logged out of facebook - please do know the solution must by in ruby.

i have a few emails with the author and it looks like the only situation here is to catch the exception thrown by current_facebook_user.fetch. If it throws an exception most likely that user has log out of facebook.