2.2.6.2.7 proxy-revalidate

This directive specifies that if the cache is a proxy server, it MUST revalidate that the content is still refreshed before it is streamed. The directive does not apply if caching has been disabled by using the no-cache (section 2.2.6.2.3) directive or the private (section 2.2.6.2.6) directive. The proxy-revalidate directive MUST be ignored by caches that are not acting as proxy servers.