Logging out issues

["JordonShaw" <webforumsuser@xxxxxxxxxxxxxx>]

I'm having a issue where whenever my users log out, they really don't logout.  
Their login is cached and until they delete all of their browser items, they 
are still logged in.  What type of code do I need to use to have them actually 
log out when my logout script runs, and not make them have to clear everything 
in their browser?

 Thanks,
 Jordon