For ldiskfs-based backend, the OI scrub scans the local device linearly. It iterates all the inodes on the ldiskfs partition in the inode tables in each block group without distinguishing whether the block group that contains the inode table has been initialised or not. In fact, to speed up the mke2fs and local e2fsck, the ldiskfs supports "uninit_bg" feature that allows to create the backend-filesystem without initializing all of the block groups, then dramatically reduce e2fsck time.

So for the iteration used by the new LFSCK (including backend OI scrub), it should also make use of such feature to skip uninitialised block groups to optimise the scanning.