I make reference here to the Wikipedia article on the Fiscus Judaicus, or similar background.
The question here is: is it likely that Domitian’s niece, Flavia Domitilla; her husband, Titus Flavius Clemens; and their sons were executed/wiped out in 95 CE because Flavia and Clemens were participating in Judean religion?
I respond: Domitian had known for years that Flavia and Clemens were participating in a Judean-based sect. Their sons were being educated in Domitian’s palace! Furthermore, during her lifetime, Flavia had donated catacombs to her sect/congregation; these catacombs were the earliest Christian catacombs in Rome. If I am correct that her congregation was the same as Mark’s, we can infer from the Gospel of Mark that she did not observe kosher laws (“all foods are clean”), and she did not follow strict Sabbath rules. And the congregation had long ago jettisoned a concern for the earthly Temple in Jerusalem and replaced it with a focus on Jesus as a heavenly intermediary. We can also assume that as a niece of the emperor, she would not neglect the appropriate emperor worship or required taxes.
So on what grounds could Domitian complain about Flavia’s or Clemens’s religious beliefs or practice? Domitian was grooming her sons to succeed him! The offense committed by Flavia and her family must have been so great that Domitian was willing to kill his closest relatives, and let the imperium pass out of his biological family.
I cannot infer a religious offense of sufficient gravity. It is possible that Flavia was denounced and smeared by someone with their own agenda, who misrepresented her actual activities. But she was so close to Domitian that I think he would have been able to get accurate information from her associates and household staff. I think, more likely, her religious practice was a justification for a purely political execution to pre-empt a perceived threat to Domitian’s power.