In my testing, both 'clear ip arp' and 'clear arp-cache' send an ARP request to the MAC address that last held the IP to see if it still has it. The difference I noticed is:
clear ip arp - clears the entry and sends a single request out to see if it should immediately restore the entry
clear arp-cache - sends multiple arp requests out over a minute or so, and doesn't clear the local cache until they've all gone unanswered.
My guess is that clear arp-cache did work for you, but you checked the table too quickly. I thought it was only working intermittently until I realized there was a bit of a delay.
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