How to block access for domain that doesn't exist in server

I have vps and there are many requests for one domain that do not exist (Domain's nameserver point to my vps ip)

It's likely this ip used to host for that domain and previous owner do not change nameserver

How to block this type of access because there is such amount that wasting server resource and behavior is likely apache ddos to my vps

I need to block them on network level because block in webserver level still waste resource and apache slot is filled up fast and reach maxclients.

Thank you

http://ift.tt/1dvHQ0Z