According to the nineteenth-century historian, William Berry, Guernsey, in 1061, was attacked by 'a new race of pirates' who
issued from the southern ports of France bordering on the Bay of Biscay. Duke William was at Valognes when he received information of this attack, and he immediately sent troops under the command of his squire, Sampson d’Anville, who landed at the harbour of St. Samson. Being joined by the islanders who had sought refuge at the Castle of the Vale and other retreats, he defeated the invaders with much slaughter. Duke William is also said to have made large concessions of land in Guernsey to d’Anville”
The reference to the pirates issuing from French ports bordering Biscay has no supporting evidence whatsoever. Perhaps someone remembered there's a village in Aquitaine called Castel-Sarrazin whose inhabitants are called Sarrazins and voilà.