What is the minimum intelligence for a cultist under Juiblex or Zuggtmoy?

In Mordenkainen’s Tome of Foes one can gain Demonic Boons for joining specific cults, changing one’s abilities, spells, resistances and even modify combat abilities. Various Demon-Lords (Juiblex, Yeenoghu and Zuggtmoy specifically) also offer an ‘equal penalty’ for intelligence, wisdom & charisma (though Yeenoghu leaves ‘wisdom’ untouched) – and this penalty can be quite severe. Given a loss of four to eight points many otherwise-enthusiastic cultists are left quite mindless, which is the point of the cult, story-wise. But what is the minimum? Inquiring minds want to know:

Cultists: Just how stupid can they get?

Low-Ability History: Player Characters in 5e may have a minimum of three and maximum of twenty for any ability score. Note that previous editions even had negative ability scores, especially charisma (this gave fear-aura abilities) – but such a mechanic is not in 5e. Many automatons, oozes and slimes in the first edition of AD&D had ‘non-intelligent’ or a zero-intelligence score – but with 5e even iron golems have a surprisingly clever score of 3. Even ‘utterly mindless’ (i.e. ‘actually devoid of all brain-matter’) undead non-player skeletons only have a penalty of -4 (DM’s Guide p.282).

So, just to specify &/or reiterate: Do cultist-creatures (humanoid or otherwise) have a minimum intelligence score, if any?

Reason for asking: Many spells focus easily on targets with low ability scores, especially those with low wisdom – this would change game-play. Also, if any creature’s lowest score was below that of a Violet fungus, the target may enter a non-ambulatory &/or vegetative state. If this reduction were allowed to go below zero, one must assume instant death for any such gormless person joining such cults (this is a very possible and reasonable ruling – demonic cults are not known for their kindness nor protection of specific minorities). Thus, any rulings – even Crawfordonian ones – would be welcome.