Homegroup is asking to join a Homegroup that isn't there....

I build machines and sell them whenever someone I know needs one, but I replace the hard drive when I sell it and rebuild the system exactly the same every time using this HD. I like the system, and it works fine for me doing it like this. I am on the fifth or sixth reincarnation of this machine and I am now trying to create a homegroup for all of my machines at the house (currently 5, three desktops and 2 laptops) and it keeps saying that an OLD machine, one that isn't even around anymore has created a Homegroup and asks if I want to join it. The machine name isn't here, it's been gone for a while. How can I get it to "forget" this computer so I can create a new homegroup to add all of the new computers to?