Searching a package repository generates custom responses based on the request. Therefore, search results are not well suited for being cached. The depot server sets the appropriate HTTP headers to make sure search results do not become stale in a cache. However, the expected bandwidth savings from caching are small. The following partial httpd.conf file shows how to specify not to cache search results.
<LocationMatch ".*/search/\d/.*"> Header set Cache-Control no-cache </LocationMatch>