Grub cd!
 

Is there any CD or DVD which just has GRUB and which corrects Grub errors? For example if someone installs a Linux distro and its grub boot loader does not work and has errors, he could just install fresh GRUB from an independent GRUB CD/DVD which detects one of two Linux distros. Or with the help of GRUB CD/DVD one could correct errors in GRUB installed by some Linux distro? Kindly inform? :)

Yes, think this is what you want:
http://www.supergrubdisk.org/