Thank you, mMagme, you made good points.
I wonder if network calibration is needed, my initial idea was to use a classifier with standard training settings.
I see it may become overconfident on domains with fuzzy borders due to the random factors.
In my original setup, the probabilities for all other domains remain over 0.9 in softmax output and for artificially split domains 0.5-0.7
Using special techniques for calibration may deviate from my experimentation plan since I use that classifier for illustrative purposes.
Anyway, I will try soft labeling it if it’s easy to apply.