AR Denarius Of Domitian. Damnatio Memoriae?

No. Damnatio Memoriae would have obliterated his name, as well as his face. The face would also have been erased more thoroughly and utterly. Plus, the reverse figure on this coin is Pegasus, who is suffering from no such proscriptions, yet has the same deep scratch-mark through it.

Silver coins, generally, don't show much evidence of damnatio happening. The relative ease with which silver and gold coins could be melted and reminted, means any coins withdrawn under the damnatio would have been melted down, rather than officially defaced. It's almost always bronze coins that tend to show evidence of damnatio.

Which leaves the explanation of the deep scratches. To me, they look more like "plough damage" or "trowel damage", rather than ancient test-cuts. The freshness of the cuts,the ragged edges of the cuts where the chunks of silver torn away are still hanging on to the coin, clearly indicate the coin did not circulate after the damage was done.

I agree -
Metal detecting jargon:
heartbreaker - A high quality coin or artifact that is found, but something bad is wrong with it (such as a digger scratch, or damage from a plow.)