Clearing DNS caches on Mac OS X
When making DNS changes, sometimes it is difficult to see the results from your own computer, because there are many caches involved that hold on to the last queried IP for the given host name. On Mac OS X dscacheutil can flush the DNS cache.
Sometimes, however, this isn't enough. In extreme cases you may have to kill the DNS responder.
sudo killall -HUP mDNSResponder