Support Articles ID for Current schedule DB release DB and OCR recovery

Release Schedule of Current Database Releases refer note [ID 742060.1]

How to restore ASM based OCR after complete loss of the CRS diskgroup [ID 1062983.1]
How To Rename A Diskgroup On ASM 11gR2? [ID 948040.1]
A diskgroup can only be dropped if it can be mounted.
If you cannot mount it anymore (like in your case) the only way to 'delete' the diskgroup is to clean up the involved devices
using OS command 'dd'.

An example for this cleanup task is:

# dd if=/dev/zero of=/dev/ bs=1M count=100

It is sufficient to cleanup the first 100 MB on each affected devices. After all devices are cleaned in that way the diskgroup is not longer existing
and can be re-created using the clean devices.

After the diskgroup is re-created you can restore OCR and database.