State Management :: Clear Private Static Collections?

I am working on rewriting an application. The previous developers have declared some Private static hashtables within a class in a class library. The first time when the application runs, this hashtable gets populated by running the query. After that this hastable is refrenced elsewhere to get the employee information.Even if the employee is removed from the DB, he is still able access the application, Since the private static hashtable holds the employee information. I totally understand that the hashtable is referenced to prevent the DB calls everytime.

The problem is even after closing the browser and restarting the application the hashtable holds the employee information. How do i get clear this so that it calls the DB?