Apple flushdns tool

DNS requests are usually cached, this is great as it speeds up the lookups on your machine. Occasionally you might want to clear out the cache though, using terminal its very easy to do.

MAC OSX 10.4 And Below:
lookupd -flushcache

MAC OSX 10.5 And Above:
dscacheutil -flushcache 

Tip: To launch terminal click on spotlight & type terminal.