as simple as that:
arp -a
arp -n
arp is now deprecated in favor of ip utils, this is the equivalent command
ip neigh showARP table might contain (incomplete) entries, these are not a problem and not present in the arp table any more (read: https://serverfault.com/questions/476272/arp-delete-is-not-deleting-an-entry-merely-marks-entry-as-incomplete), so just wait until the system removes them. If you want to force them out anyway you need to explicitly flush out the arp table by clearing it, just do this if you know what you are doing
ip link set arp off dev eno1
ip link set arp on dev eno1
You can remove a single entry just by typing:
arp -d 192.168.1.1
arp utility does not accept an option to clear the full cache
with ip utility you may do something more useful if you need to clear the whole cache, something like that:
ip -s -s neigh flush all
The first -s will provide a more verbose output. By adding one more, we can select the neighbor table, if your ip utility doesn't support the -s flag just remove it