OS X Yosemite 10.10

Clear MDNS (Multicast DNS) and UDNS (Unicast DNS)

sudo discoveryutil udnsflushcaches

sudo discoveryutil mdnsflushcache


OS X Mavericks 10.9

dscacheutil -flushcache; sudo killall -HUP mDNSResponder


OS X Lion and Mountain Lion 10.7 and 10.8

sudo killall -HUP mDNSResponder


OS X Leopard and Snow Leopard 10.5 and 10.6

sudo dscacheutil -flushcache

All flavors of Windows:

ipconfig /flushdns