I am using Windows 8.1, but I finally think I have a way : it worked to remove the stale HomeGroup when nothing else could. Not a solid procedure, but here goes :
1) stop the three "Peer ..." services
2) stop the two "HomeGroup ..." services
3) stop the "PNRP ..." service
4) delete the contents of %Windir%\ ServiceProfiles\ LocalService\ AppData\Roaming\PeerNetworking
5) forget your network, if wireless, and disconnect
6) navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HomeGroupProvider\
7) delete the contents of ServiceData and LocalUserMembership
8) navigate to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\HomeGroupListener\
9) delete the contents of ServiceData