Cyclopean Tomb, for example, creates an effect that continues for the rest of the game, even if it is destroyed.
Is there a name for the conceptual "board" of lingering effects whose originating cards are no longer on the battlefield?
They do not reside in any special realm. They just continue to apply. CR 611.2a states
A continuous effect generated by the resolution of a spell or ability lasts as long as stated by the spell or ability creating it (such as “until end of turn”). If no duration is stated, it lasts until the end of the game.
What is interesting is, that these effects continue to apply even if the controller of the spell or ability that generated it leaves the game in a multi-player. So, if you turned some of your opponent's lands into swamps and then are killed, those lands continue to be swamps as long as they remain on the battlefield with the counters. Since you already left the game, your turn will be skipped and no counters are removed by the tomb's second ability.
Most cards with lingering effects have had their oracle text changed to include "emblems", which goes into the Command Zone (example: Elspeth, Knight-Errant), however the Cyclopean Tomb is not one of them (likely due to them being unused in competitive formats).
Because Cyclopean Tomb doesn't mention an emblem, Rule CR 611.2a would apply.
Here's a good article to read about this specific issue: