$ git clone -n https://src.fedoraproject.org/rpms/R-orcutt.git /var/lib/mock/f42-build-side-1-3501314-45974/root/chroot_tmpdir/scmroot/R-orcutt
Cloning into '/var/lib/mock/f42-build-side-1-3501314-45974/root/chroot_tmpdir/scmroot/R-orcutt'...
$ git fetch origin 48a4bb04d576ee1d7ae4b71f1818bee32ec51e9c:KOJI_FETCH_HEAD
From https://src.fedoraproject.org/rpms/R-orcutt
 * [new ref]         48a4bb04d576ee1d7ae4b71f1818bee32ec51e9c -> KOJI_FETCH_HEAD
$ git reset --hard KOJI_FETCH_HEAD
HEAD is now at 48a4bb0 R-maint-sig mass rebuild