The following command when entered in GRUB prompt will list out the drive in which GRUB stage 1 is intalled:
grub> find /boot/grub/stage1
for me it resulted in:
(hd0,5) ------> internal 80 GB SATA
(hd1,0) --------->External USB Western Digital passport
This was because earlier I had grub on internal hard disk which I erased from MBR. And second was for the USB Western Digital passport drive.
One other command that is helpful is:
grub-install --recheck /dev/sdb
This installs grub on the selected drive, WD in my case.
But for a fool proof method use root and setup commands from inside grub prompt to install grub.