How to clear DNS cache in OS X 10.10.5?

You may also download CleanMyMac. It provides a nice interface for flushing DNS cache.

For more details, you may refer to: http://couponhacks.org/easiest-way-flush-dns-cache-mac/

HowTo article from Apple

https://support.apple.com/en-us/HT202516

Note: I have never tested this.

In Terminal.app, type

sudo killall -HUP mDNSResponder