For Classic XR (32-bit) if you are running version 6.5.3 with Rommon version 10.69, there is a command in Rommon mode which will do the wipeout of the HDDs.
rommon 2 > priv
You now have access to the full set of monitor commands.
Warning: some commands will allow you to destroy your
configuration and/or system images and could render
the machine unbootable.
rommon 3 > hderase
SATA HD(0x4,0x0,0x0):
Model : SMART SATA SHSLM32G3BCITHD22
Serial No : STP21299D3C
Secure Erase Supported
Security State : Disable/Not Locked/Not Frozen
All the contents on this Drive will be Erased
Do you wish to continue?(Y/N)Y
Erasing SATA HD(0x4,0x0,0x0)...
Erasing SATA HD(0x4,0x0,0x0) Completed
SATA HD(0x5,0x0,0x0):
Model : SMART SATA SHSLM32G3BCITHD22
Serial No : STP21699CRP
Secure Erase Supported
Security State : Disable/Not Locked/Not Frozen
All the contents on this Drive will be Erased
Do you wish to continue?(Y/N)Y
Erasing SATA HD(0x5,0x0,0x0)...
Erasing SATA HD(0x5,0x0,0x0) Completed
rommon 4 >