It seems mDNA U5 and its subclades first arrived into Europe via Greece and Spain:
"The presence of haplogroup U5 in Europe pre-dates the expansion of agriculture in Europe. Bryan Sykes' popular book The Seven Daughters of Eve says it shows up 45,000-50,000 years ago in Delphi, Greece and named the originator of haplogroup U5 Ursula. It shows that U5 is the first out of Africa into Europe, and that it shows up as the first Europeans in two places, Delphi and Spain around 50,000 years ago."
So its presence in your genetic marker does not neccessary mean it was via invasions of Normans given Greece is one of the original European locations this haplogroup arrived in. Also recent DNA test reveal the discoveries in mDNA Grave Circle B of early Bronze Age Mycenaean skeleton remains show their mDNA belonged to haplogroups UK ("heart-shaped face" individuals Ã55 and Ã58, possibly brother and sister), U5a1 or U5a1a ("long-faced" individual Æ59) and the Cambridge Reference Sequence ("heart-shaped face" individual Á62), which is "compatible in the region sequenced with various haplogroups including H, HV1, J, U, U3, U4 (UK, U5a1 or U5a1a)." http://img221.imageshack.us/img221/7601/reconstructionsmycenaegxd2.jpghttp://img221.imageshack.us/img221/7601/reconstructionsmycenaegxd2.jpg http://www.guardian.co.uk/science/2008/jun/01/genetics.sciencenews?gusrc=rss&feed=networkfronthttp://www.guardian.co.uk/science/2008/jun/01/genetics.sciencenews?gusrc=rss&feed=networkfront
So your ancestry might be traced back to Mycenaean Greeks rather then Norman invadors. LOL!! ;-)