Logout Facebook via clear session and cookies

I hv an app that use FB login, but this app can be use by many user in the same device, so i need to totaly logout user from fb and allow other ppl to signin with their fb.
would u help me how to do it?
the problem is that when the firs user logout, the second user cannot see the login menu to enter !
i hv to remove the cookies to to that but i canot find anysolution more?
regards

local facebook = require “facebook”

– listener for “fbconnect” events
local function listener( event )
if ( “session” == event.type ) then
– upon successful login, immediately logout
if ( “login” == event.phase ) then
facebook.logout( ) – >> this code only logout the user but new user cannot login if if login again!!
end
end
end

– first argument is the app id that you get from Facebook
facebook.login( “1234567890”, listener ) [import]uid: 220888 topic_id: 37552 reply_id: 67552[/import]