Can a noncreature artifact be destroyed by reducing toughness?
The Gods from Theros aren't creatures sometimes.

208.3. A noncreature permanent has no power or toughness, even if it’s a card with a power and toughness printed on it (such as a Vehicle).
208.3a If an effect would be created that affects the power and/or toughness of a noncreature permanent, that effect is created even though it doesn’t do anything unless that permanent becomes a creature.

Thus, they have no power and toughness that can be reduced to below 0.