What is Varnish? Don't think you hit this link accidently but here is some introduction for the newbies.
Varnish is an HTTP accelerator designed for content-heavy dynamic web sites. In contrast to other HTTP accelerators, such as Squid, which began life as a client-side cache, or Apache, which is primarily an origin server, Varnish was designed from the ground up as an HTTP accelerator.
More descriptive video:
Okay, now how to flush the varnish cache. Run the belwo command. You don't need to restart the demon.
varnishadm -T 127.0.0.1:6082 url.purge .
Simple as that.