An ARP reply is generated only if the destination protocol IP address is reachable from the local host, as determined by the routing algorithm, and the next hop is not through the same interface. If the local host functions as a gateway, this can result in ARP replies for destinations not in the same subnet. This shows that to drop the ARP request is justifiable.
Troubleshoot Address Resolution Protocol (ARP) or Content Addressable Memory (CAM) table-related issues on Catalyst 6500/6000 Switches.
For further information click this link.
http://www.cisco.com/en/US/products/hw/switches/ps708/products_tech_note09186a00807347ab.shtml#dfc