Open Terminal and run this command
dscacheutil -flushcache
TTL and DNS cache
Time to Live (TTL) is used to renew the DNS records on all the DNS servers around the world to the set TTL value.
The units used are seconds. The older common TTL value for DNS was 86400 seconds, which is 24 hours. A TTL value of 86400 would mean that, if a DNS record was changed on the authoritative name server, the DNS servers around the world could still be showing the old value from their cache for up to 24 hours after the change.
Why change the TTL value
If you want to make quick DNS changes, it is a good practice to place a low TTL value. The TTL values can be changed by logging in to the the Self Service Center.
If you change the TTL, you have to wait for the current TTL to pass before the new TTL will be active. This means that if you change the TTL to 1 hour instead of 24 hours, you have to wait the 24 hours first before the 1 hour TTL wil be active.
Setting a TTL value lower than 12 hours is not recommended, and should only be used during a short period for special cases. By default, the TTL value is 24 hours.