I know that hindering terrain can't be destroyed, but can I attack a piece of hindering terrain, or a hindering terrain marker, and turn it to debris?

Here are a couple of potential examples that describe why it would matter:
1. GSX Magneto turns a bush into debris then stands on it to increase his combat values.

2. A GOW3 ink grenade is tossed into the middle of my team, it does its initial damage, and turns into a hindering terrain marker for a turn. If I can turn it to rubble or destroy it, I avoid damage on the next turn.

Any thoughts?

Just like you said, Hindering terrain cannot be destroyed, so no that will not work.

No you cannot.

But you can use Moleman or Cave Carson to get a debris marker in hindering terrain.

Also, the ink grenades effect is not linked to the hindering terrain marker, so even if you do remove it somehow (there are several special powers that can do it) it still doesn't prevent the penetrating damage from happening.

Because, sometimes, you want terrain that is more hinderinger.

I want terrain that is the hinderingest.

If the marker created by the grenade is gone, how does it still cause the second round penetrating damage?

INK (1 penetrating damage): Place a hindering terrain marker in the target square. At the beginning of your next turn, deal 1 additional penetrating to each character occupying the target or adjacent squares, then remove the marker.

The damage effects the target square + adjacent, not the Hindering Terrain Marker + adjacent. It doesn't matter if the Hindering marker disappears, only who is in/next to the Target Square at the beginning of your next turn.

Not caring about the hindering part. It could be the most hinderingest of hindering terrains. Fill the square full of angry bees attacking kittens. Just want to be able to destroy or throw the hindering terrain token back at Gen Raam when he flings an ink grenade in the middle of my team.

Good explanation. Did not catch the target square part, the first time I read it.