You're debugging some DNS changes in your network and Safari (or curl / any other tool) keeps sending requests to an old DNS entry?
With these commands, you can clear your system's DNS cache:
| macOS version | command |
|---|---|
| 12 (Monterey) | sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder |
| 11 (Big Sur) | sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder |
| 10.15 (Catalina) | sudo dscacheutil -flushcache; sudo killall -HUP mDNSResponder |
| 10.14 (Mojave) | sudo killall -HUP mDNSResponder |
| 10.13 (High Sierra) | sudo killall -HUP mDNSResponder |
| 10.12 (Sierra) | sudo killall -HUP mDNSResponder |
I hope this helps 🙂