The source MIB provides only a placeholder DESCRIPTION for this object, but its name and defined values make its purpose reasonably clear: it's an action object used to clear the switch's ARP cache, staying at idle(1) normally and accepting a write of clearCach(2) to trigger the clear. Administrators use this when stale or incorrect ARP entries are causing connectivity issues and they want to force the switch to relearn IP-to-MAC mappings from scratch. For example, setting this object to clearCach(2) after replacing a server's network card, and thus its MAC address, would immediately flush the switch's old ARP entry for that device's IP.