I'm a bit late here, but the fluff has also advanced since this question was asked. Spoilers ahead concerning a certain psychic Inquisitor who lives in a chair.
In the Ravenor series, Inquisitor Ravenor finds the drug-addicted Zael Effernetti while investigating said drugs. Though he initially uses the child to find a local dealer, Ravenor keeps him around due to his terrifying latent psychic potential. Ravenor identifies Zael as being a mirror - a psychic that can reflect the psychic energies of those around him, or something like that. Ravenor himself is a very powerful psychic, but even so is unsettled by Zael's sheer potential.
Because of reasons (don't want to spoil too much), Zael entered a deep coma. Ravenor thought he was dangerous (more reasons), so he had Wystan Frauka, a pariah that worked with Ravenor, tend to the comatose child, effectively nullifying Zael's psychic abilities.
Except, it didn't.
In spite of being literally inches away from a pariah, Zael was such a powerful psychic that he was able to psychically communicate with Wystan! What's more, Zael's psychic presence was apparently so powerful that he permanently burned out Wystan's Null abilities! What's more, the effect seems to have been permanent, with no indication otherwise.
It should be noted that Wystan had successfully blocked multiple alpha level psychics, including Ravenor, on several occasions before this. There is no question whether Wystan's abilities were effective.
As for Zael... he was given to the Grey Knights and eventually became the Grey Knight Hyperion, the guy who broke Angron's sword.
Since this is a Black Library source, it canonically establishes that a Blank can be affected by psychic shenanigans if the psychic is strong enough. Just, the sheer power needed for this appears to be enough to put even an alpha level psychic to shame. More than that, it canonically establishes that a Blank's abilities can be permanently extinguished by a strong enough psychic.
In any case, I suspect this also answers the question of how Magnus and THE EM'PRAH were able to operate with the Sisters of Silence around.
TLDR: Black Library source with a psychic speaking psychically to a Blank and then burning out his Blankness.