So, as a reminder, to flush the DNS cache in Mac OS X 10.5 and 10.6, run this command in Terminal:
sudo dscacheutil -flushcacheTo do the same in 10.7 and 10.8, run this command:
sudo killall -HUP mDNSResponderAs Apple points out, you might need to do this in the following situation:
"OS X keeps a local cache of resolved DNS queries for a time defined by the DNS server, but sometimes it may be necessary to reset the cache immediately and re-query a DNS server. For example, you might do this after an entry on the server is changed or a new entry is added."