$ git clone -n https://src.fedoraproject.org/rpms/perl-Cache-FastMmap.git /var/lib/mock/f41-build-816514-150225/root/chroot_tmpdir/scmroot/perl-Cache-FastMmap
Cloning into '/var/lib/mock/f41-build-816514-150225/root/chroot_tmpdir/scmroot/perl-Cache-FastMmap'...
$ git fetch origin 1738b74ae0274e8a284a0c9d7b0b62524f1c9bc7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/perl-Cache-FastMmap
 * [new ref]         1738b74ae0274e8a284a0c9d7b0b62524f1c9bc7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 1738b74 Perl 5.40 rebuild