With the release version of 1.8d and its accompanying 'wa', you can
go to whatever URL corresponds to 'wa' on your machine and invoke it
with a ?RESET-COOKIE parameter.  For instance

http://your.machine.com/cgi-bin/wa?RESET-COOKIE

Again, this only works with 1.8d release 'wa'.  (It might work with
some late beta 'wa's but I have no idea which ones.)  Note that this
is not a third-party operation, in other words, you as the LISTSERV
maintainer cannot invalidate someone else's cookie this way.

The only other way to invalidate a cookie would be to change or delete
the LISTSERV password associated with the login ID being used from the
browser.

Nathan