The completion of labor to my residence occurred on December 2, 2020 and a Notice of Intention to Claim was sent to me March 17, 2021. Statement and Notice of Mechanics Lien was filed with county clerk March 31, 2021. The contractor was paid in full but did not pay the subcontractor due to unsatisfactory work. The subcontractor in turn initiated the lien on my home. Subcontractor recently contacted me to inform of lien foreclosure.
First, how did the subcontractor contact you? If it was service of a lawsuit, contact an attorney immediately. If you don't answer and raise your defenses, you could end up with a judgment against you even if the lien is not valid.
While I am unable to determine whether the lien is technically valid or not based only on your question, my first consideration would be whether your project qualifies as an owner-occupied residence.
"Foreclosure" isn't a common word to throw around unless a foreclosure lawsuit has been filed or is going to be filed. They have one year from the date the lien was filed to start a foreclosure lawsuit on the lien.
If this qualifies as an owner occupied residence, and you paid the GC in full for the work of the subcontractor prior to receiving the notice, they do not have a valid lien. In that case, if they file a lien foreclosure lawsuit, your attorney would likely deny liability and raise a counter claim for slander of title.