Linux btrfs how to remove unexistent filesystem from list?

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http://unix.stackexchange.com – I'm giving a try to btrfs. As newbie I did some mistakes, which are good for learning! I created several btrfs filesystems upon different devices (sdX, loop, lvm, etc). During these tests, I removed (abruptly) some or all devices which were part of a btrfs filesystem (fs were unmounted first). But now, command btrfs show still shows filesystems UUID and list of devices. I understand that I should have done a btfrs device del BEFORE removing devices... But where does btrfs stores its list of handled filesystems? Is there a conf file somewhere? A special command in btrfs-tools? I didn't come (HowTos)