What happens if someone steals my plots and my private key?

[Zahk]

I have answered it here:

Compromised plots and double-farming detection

Here’s a thought experiment… Let’s say I suspect my data, including plots and private keys, to be compromised. Let’s say I am not 100% certain, and certainly not to the point of throwing away $xx,000 worth of plots based on suspicion alone. Is there a way, theoretically speaking, that I, as a farmer, can detect that my plots are being “double-farmed”? (edit to clarify: farmed at the same time by somebody else)