If you ever need to flush the DNS cache of Mac OS X there are several command lines to do so or a little utility
If you wanna use a simple software you can try DNS Flusher but there website isn’t really clear on which versions of Mac OS it supports.
Otherwise you’ll find here Apple’s official instructions all using the “Terminal” application.
Under OS X Yosemite and OS X El Capitan
Use the following command under Terminal to reset the cache : OS X Yosemite 10.10.4 and El Capitan Beta
sudo killall -HUP mDNSResponder
Under OS X Yosemite 10.10 to 10.10.3 :
Use the following command under Terminal to reset the cache :
sudo discoveryutil mdnsflushcache
Sous OS X Mavericks, Mountain Lion et Lion
Use the following command under Terminal to reset the cache :
sudo killall -HUP mDNSResponder
Mac OS X 10.6
Use the following command under Terminal to reset the cache :
sudo dscacheutil -flushcache