No — not a major grave sin if there is no sexual desire and it is only for removing itching or discomfort.

In Jain dharma, the inner intention matters most.

• If there is no lust, no sensual intent, no attachment, then it is not a very grave sin.
• But touching the private parts should still be done carefully, with restraint and awareness, because it can become a cause of impurity, carelessness, and subtle attachment.

Strict answer:

• Major grave sin? No.
• Improper / avoidable act? Yes.

If done only for physical need and without desire, it is not the same as sexual misconduct in Jain understanding.