Once you are logged with IIS, how can i logout user ??

I use the following method to authenticate user on the web site :
request.servervariables("AUTH_USER")

but when the connection is timeout and i recall the the default page to enter the login and password, it does not work.

i believe that the request.servervariables("AUTH_USER") are not reinitialize and the user are not really logout
then how can i reinitialize this object ?? without closing the explorer and come back on the site.

thanks....vince