I was recently revamping the storage layout on a CX4 and needed to delete all the raid groups.  I had already removed the LUNs from all storage pools and deleted the LUNs, which caused most of those raid groups to show as “Unbound” as it should have:

 

I delete all the raid groups in one operation by highlighting them and clicking Delete.  All but three went away.  One remained showing as raid 5, the other two showed as Unbound.  Trying to delete them produced a message like the following “RAID Group 6 – Object already requested for delete. Please wait for a response from the Array”

I was not able to get them to delete.  I waited a day just to see what would happen.  I rebooted both storage processors.  Finally, what I ended up doing was editing their properties, which it still allowed me to do, and set each of them to auto delete upon deletion of the last LUN.  Then, I created three new LUNs based on these three problem raid groups.  Waited a few minutes, then deleted the LUNs.  That caused the raid groups to go away finally.