Q. I'm trying to wipe clean a hard drive. No matter what I do, I can't get rid of this GRUB on my screen. How do I wipe it out?
A. You have to delete the master boot record on the disk. Regular format will not do it.
I am using Live CD for Ubuntu 18.04 LTS (Bionic) for this experiment.
If you are working under Linux, this is the command to clear it (Be careful, running those commands can mess up your working hard drives, if you don't specify the proper device):
# dd if=/dev/zero of=/dev/sda bs=512 count=1
If you have access to Windows/MSDOS tools:
fdisk /mbr
OR
fixmbr [device_name]