libvirt users - Apr 2017 - Proper way to remove a qemu-nbd-mounted volume usnig lvm

I either haven't searched for the right thing or the web doesn't contain
the answer.

I have used the following to mount an image and now I need to know the 
proper way to reverse the process.

    qemu-nbd -c /dev/nbd0 <qcow2 image using lvm>

    vgscan --cache    (had to use --cache to get the qemu-nbd volume to
    be recognized, lvmetad is running)

    vgchange -ay

    lvdisplay

    mount <selected qemu-nbd related 'LV Path' found from lvdisplay
    above> <mount point>

I have done the following:

    umount <mount point>

    lvchange -an <all qemu-nbd related 'LV Path's found from
lvdisplay
    above>

    vgchange -an <qemu-nbd related volume>

Now what?  How do I get the volume out of the list so I can use 
'qemu-nbd -d /dev/nbd0' to dis-associate the image with /dev/nbd0?  
vgreduce seems to be for volumes which have multiple underlying 
devices.  I started to use vgremove but, when it started prompting for 
confirmation about removing logical volumes, I wasn't sure exactly what 
it was going to do and responded 'no'.

If there is a web reference explaining this specific situation just 
point me to it - I'm not opposed to reading.  Thanks for the help.