/etc/hosts does not use DNS at all so talking about DNS cache makes no sense. This file is authoritative over DNS concerning name resolution, as specified in /etc/nsswitch.conf (the Name Service Switch config file).
So if you enter a IP-host mapping in /etc/hosts it will always take precedence over DNS. (Of course, unless you modified /etc/nsswitch.conf, and you should have a good reason to do so.)