You probably have the same chance of negro heritage as Rob. The Italians belong to the same haplogroups as the rest of the europeans. However, there was a migration of arabs from north africa to southern italy around the time of the fall of the roman empire. So a small minority of italians have maybe 1% arab DNA.
Racists looking to denigrate italians turned "some italians have very minute amounts of north african (arab) dna" into "all italians descend from negroes." But north african arabs are not negroes.
And....someone that is 99% european and 1% arab did not "descend from arabs." They descended from europeans but have a minute amount of arab dna.