I don't know how well this works in practice, but it appears HTTP clients can force a check with the origin server if needed: http://www.w3.org/Protocols/rfc26

I don't know how well this works in practice, but it appears HTTP clients can force a check with the origin server if needed: http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html "...request with a "Cache-Control: max-age=0" directive (see section 14.9), to force a check with the origin server."