Instances are still running on the compute nodes after they are removed from Nova

Issue

• There is an inconsistency between the nova and kvm reporting in regards to the number of VMs running on the cluster. Nova shows very few VMs running, while kvm shows a number of times more.
• VMs were deleted using the dashboard and nova command line. However, days later checking virsh list on the compute nodes showed some of the deleted instances were still running on compute nodes from libvirt/KVM. How can I make sure that all VMs are removed by nova from libvirt?