When attempting to /clone distant blocks to current location, the game responds with "Cannot access blocks outside of world". This occurs even when another player is standing at the distant location (chunks are loaded).
Alternate player stands at x:1000, z:1000.
Test player stands at x:2000, z:2000 and executes the following command:
/clone 1000 2 1000 1000 2 1000 ~ ~ ~
Result: "Cannot access blocks outside of world"