You're on the right track with dd, but that will only remove the partition table...the data is still on the disk as you are overwriting the first 512 bytes of the disk which is only the MBR. If you want to blank the whole disk remove the bs and count options.
If you are supposed to be wiping the machines to get rid of sensitive data I would suggest having a look at DBAN
Darik's Boot and Nuke (Hard Drive Disk Wipe)
It overwrites the data in multiple passes so that it can never retrieve. It exceeds US government requirements for disk cleansing and is really excellent.