How to make pages expire after logout

I have an application which is basically a MySQL CRUD application. Everything works fine so far but I just discovered that when a user logs out and clicks the back button on the browser the logged in pages reappear. I know this is not right because when a user logs out the entire session is supposed to expire, and if the browser back button is clicked instead of reopening the last pages it should prompt the user to log in again. I do not know much about sessions in php and I would like someone to help me out here. What do I need to do to rectify this problem of non-expired sessions? I am using PHPRunner version 5.2 (Build 4905) and my server environment is Zend Server Community Edition 5.0.0 with IIS 7.5 on Windows 7 32bit. I will appreciate any and all help anyone can render in this case.

Thank you all in advance.