Can't remove root volume for DR SVM vserver

I've test SVM DR - it works and now I want to clean up the mess I've made. I've removed the peer relationships, deleted all but the root volume, but now I can't remove the root volume so I can delete the SVM:

mycluster::> vol destroy -vserver mydrtest -volume mydrtest_root -force true

Error: command failed: This operation is not permitted on a Vserver that is configured as the destination for Vserver DR.

And of course just attempting to delete the vserver as is fails as a result:

mycluster::> vserver delete -vserver mydrtest

Error: command failed: Failed to delete Vserver mydrtest. Reason: Cannot delete Vserver "mydrtest" because
       there are objects associated with the Vserver that are not associated with any other Vserver:
       Volumes: 1
       Mirrors: 0
       Kerberos-enabled LIFs: 0

       Remove these objects, then try the command again.

As you can see though the only volume remaining is indeed the root volume:

mycluster::> vol show -vserver mydrtest
Vserver   Volume       Aggregate    State      Type       Size  Available Used%
--------- ------------ ------------ ---------- ---- ---------- ---------- -----
mydrtest
          mydrtest_root
                       aggr2_svmdr_testing
                                    offline    RW          1GB          -     -

Advice?