log out user with 401

Hi The PHP manual says, "Both Netscape and Internet Explorer will clear the local browser window's authentication cache for the realm upon receiving a server response of 401. This can effectively "log out" a user, forcing them to re-enter their username and password. Some people use this to "time out" logins, or provide a "log-out" button." But if you pass a 401 to a netscape client already authed, netscape pops up a window complaining that auth failed and asks the user if he wants to try again. Is there any way to clear the auth cache without netscape popping up this complaint? Thanx, Jan