For some reason there is not a command that you could run to flush the local DNS cache on macOS. However there is a simple workaround to get clear the cache by killing the DNSresponder service 🙄 ….. but I always forget what the exact command is.
sudo killall -HUP mDNSResponder
What I did is created a little shell script named flushdns, make it executable and copied it over to /usr/local/bin (note: /bin is not user writable, trust me I have tried it 😉 ).
If you are really lazy, you can copy the script over from GitHub, or just copy paste it from here.
#!/bin/sh sudo killall -HUP mDNSResponder
Now open a terminal window and just run flushdns, it will ask for your password because of sudo and the dns cache will be flushed!
Hope this helps to reduce your frustration a bit 😀