Deleting a PIV Data object can be accomplished by writing an empty object to the PIV card.
piv-tool --admin M:9B:0C --object 0101 --in empty-piv-file.dat
empty-piv-file.dat is a binary file with the content "5300". The file is attached to this article. This indicates an empty object for PIV.
The object id 0101 is the Container ID for the X.509 Certificate for PIV Authentication. I.e. the certificate
corresponding to the 9A key.
For a full list of Container IDs see: NIST Special Publication 800-73-4 Part 1, Section 3.5, Table 2. Data Model Containers.