[docker] Docker is in volume in use, but there aren't any Docker containers

I am fairly new to Docker. I was cleaning up some initial testing mess and was not able to remove a volume either. I had stopped all the running instances, performed a docker rmi -f $(docker image ls -q), but still received the Error response from daemon: unable to remove volume: remove uuid: volume is in use.

I did a docker system prune and it cleaned up what was needed to remove the last volume:

[0]$ docker system prune
WARNING! This will remove:
- all stopped containers
- all networks not used by at least one container
- all dangling images
- all build cache
Are you sure you want to continue? [y/N] y
Deleted Containers:
... about 15 containers UUID's truncated

Total reclaimed space: 2.273MB
[0]$ docker volume ls
DRIVER              VOLUME NAME
local              uuid
[0]$ docker volume rm uuid
uuid
[0]$

docker system prune

The client and daemon API must both be at least 1.25 to use this command. Use the docker version command on the client to check your client and daemon API versions.