The Address Resolution Protocol (or ARP) is a very important part of IP networking. ARP is used to connect OSI Layer 3 (Network) to OSI Layer 2 (Data-Link).
This means to communicate with any device on your network, you must have the Ethernet MAC address for that device. If the device is not on your LAN, you go through your default gateway (your router). In this case, your router will be the destination MAC address that your PC will communicate with.
To clear or flush ARP cache follow these steps:
Step 1. Open Terminal.app
Step 2. Insert this command to view whats in the cache
sudo arp -a
Step 3.a. Insert this command to delete only one interface in cache
sudo arp -d 192.168.3.1 ifscope en0
Step 3.b. Insert this command to delete whole cache
sudo arp -a -d
That is it your ARP cache is cleared