An activity performed after sex with someone to prevent your bf/gf or other partner(s) from finding out. The idea is to remove all forms of physical and circumstantial evidence that could arouse suspiscion or guilt.
These activities include, but are not limited to, intensely vacuuming the bedroom and other areas the person may have been. Using a lint roller on your bed to remove hairs, eyelashes, nails, etc, and spraying your bed with perfume/cologne. This is especially effective if you are too lazy to change the sheets. Other activities conducted in a forensic sweep include checking the bathroom for hairs, and looking for/eliminating condom wrappers (safest if cut into pieces and flushed down the toilet).
Jenny had an affair last night, but conducted a thorough forensic sweep so what her boyfriend would not find out.