Sri:
Interesting question. Swamy will answer. Additionally what is koorcham? Kai pul? Pavithram? Significance?
Because for a brahmanan this grass is more powerful even rishi vishwamithra was astonished seeing the power of grass of Vashishtha during war. Metal weapon got less power than grass.
Dasanudasan

Hare Krishna!

Aneha koti namaskaram Swami! Adiyen vaguely remembers from Swami’s Mahabarata Upanyasam that Garuda & Sarpam’s mothers fight with each other and they ask Garuda to bring Amirtham (nectar) from Indra. Garuda keeps nectar on Darpai on the way  for some time and so darpai gets cleansed, becomes sacred.

Sarvam Sri Krishnaarpanam!

Yes recently when i visited Srirangam temple, there is one Sannidhi for Kalsa hasta Garudar,  there was  printout pasted describing the reason why Garudalwar was carrying the kalasam of amritam and how Amritam dropped a bit onto Darpa grass making it sacred.

It is a very interesting story, i would suggest you to read it when visiting Srirangam.

I suppose it might described in books as described above.