[plt-scheme] how to reset help-desk's search cache?

Is there any way to reset help-desk's search cache (or whatever it's
called)?

I often find myself trying to look up details on a particular planet
package in help-desk, discovering I don't have it installed, installing
it, and trying again.  Unfortunately, help-desk can't see the new
documentation until I restart it.

Is there a way to get help-desk to see the new doc.txt file without
restarting?

Richard