$ git clone -n https://src.fedoraproject.org/rpms/nginx.git /var/lib/mock/f42-build-side-1-3586872-46926/root/chroot_tmpdir/scmroot/nginx
Cloning into '/var/lib/mock/f42-build-side-1-3586872-46926/root/chroot_tmpdir/scmroot/nginx'...
$ git fetch origin a6a0e36e7543eb70968aaf4dbd74b06213abb7c7:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/nginx
 * [new ref]         a6a0e36e7543eb70968aaf4dbd74b06213abb7c7 -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at a6a0e36 Perl 5.42 re-rebuild updated packages