Reset (not respawn) a dungeon/area to the current level

A dungeon is set at the level when you first enter, some dungeons however may have a minimum level and if you enter at a level lower then that it is set at its minimum.

An example could be a level 5 character enters a dungeon and all the monsters inside are set at an equivalent level lets say 4-6. That same character could enter another dungeon still at level 5 but it has a minimum level of 10, therefore the monsters are set to what a level 10 would find in a dungeon.

Enemies are reset once a week even in dungeons you have cleared. I am not sure if that alters the dungeons that you have entered and then left.

I can confirm that some will eventually respawn, though I'm not sure how long it might take.

What won't happen is the locations ever changing from "cleared" ; the chest in question was the dragon loot chest by the word wall in Dragontooth Crater, near Markarth. The chest had gold in it, which was a dead giveaway that I hadn't "partially" looted the chest earlier and forgotten about it. Despite the location being listed as "cleared", I had to fight another dragon to get to it.

It's not clear (and probably won't be until January w/ the Construction Kit) which chests won't respawn ever -- but in the meantime, I can verify that at least some do.