Relatively safe method, if you already have a filesystem on the drive:

1. make sure 'discard' or equivalent mount option is enabled

2. write some data to a test file

3. hdparm --fibmap testfile

4. make sure data is actually there:
sync
hdparm --read-sector <a sector number from the above command> /dev/sda

5. rm testfile
sync
hdparm --read-sector <a sector number from the above command> /dev/sda

sector should now be all 0's


Unssafe method, if there is no data on the drive that you care about:
write some data to the first sector
hdparm --trim-sector-ranges 0:1 /dev/sda
hdparm --read-sector 0