btrfs-progs-4.3.1-1.fc23.x86_64 "man btrfs scrub" says these two things: DESCRIPTION btrfs scrub is used to scrub a btrfs filesystem, which will read all data from all disks and verify checksums. and under subcommand start: Start a scrub on all devices of the filesystem identified by <path> or on a single <device>. Suggested change: DESCRIPTION btrfs scrub is used to scrub btrfs fileystems; scrub reads and verifies data with its checksums; if possible, it repairs discrepancies. Something like that.
See also: http://thread.gmane.org/gmane.comp.file-systems.btrfs/51529 especially: http://thread.gmane.org/gmane.comp.file-systems.btrfs/51529/focus=51552