With the help of Ben Collins on the silo-general list at 
lists.sparc-boot.org, this has now been resolved, and it's as simple as

dd if=/dev/zero of=/dev/sda bs=512 count=1

which is a nice, neat and elegant solution.

Many thanks to der Mouse and Martin Housemann for this assistance on this 
list.

Cheers

Gary

-- 
"There are two major products that came out of Berkeley; LSD and UNIX.
We don't believe this to be a coincidence."

BOFH Excuse #76: Unoptimised hard drive.

Linux, because eventually, you grow up enough to be trusted with a fork()