Law enforcement sources tell TMZ ... someone called 911 and reported they were hold up in the bathroom and that there were shots fired inside the house and people were either injured or dead.

There were indeed 3 people inside the house -- people working on Ashton's crib, but there was no one in the bathroom and no injured people or dead bodies.

Our law enforcement sources say cops have closed the "home invasion" investigation and now know it's a case of swatting -- where a caller tricks 911 and reports a phony crime of a serious nature, which happened recently with Miley Cyrus.

Our sources say cops believe the culprit or culprits were scoping out the home because they knew 3 people were inside. None of the 3 workers are suspects.

Ashton was not home at the time.