Only cache a dasbhoard when published

We do the same for datasets as when working on a dashboard it is
frustrating to wait for the cache to invalidate when you make a change.
The assumption when a dashboard is unpublished should also be low load
to the url.
Is that a thing? I might be being silly but I can't see it on http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9