auth-source-forget+ is a compiled Lisp function in `auth-source.el'.

(auth-source-forget+ &rest SPEC &allow-other-keys)

Forget any cached data matching SPEC. Returns forgotten count.

This is not a full `auth-source-search' spec but works similarly.
For instance, (:host "myhost" "yourhost") would find all the
cached data that was found with a search for those two hosts,
while (:host t) would find all host entries.