The answer most likely varies based on what part of the middle ages you are talking about. I can answer the question if you are discussing the early middle age (700-1000 a.d.), as McCormick in 'Origins of the European Economy' discusses coinage in the third chapter. In the early Middle Ages, you begin to see the rise of merchant cities such as Venice. These merchants of the Mediterranean would trade with Franks, Byzantines, and Arabs. Each of these large Empires had their own currency. If you look at finds of currency in Italy and also historical records, you can find that a variety of these three currencies in Italy and other locations that likely resulted from Mediterranean trade. As a noble, you would likely receive currency in what ever form was available. Your question is a Frankish noble, he would likely go with the Frankish currency, which while I can't remember the name, it would likely be the currency used. While it would seem obvious that a Frank would use Frankish currency, another important reason for that is that the Franks during this time period made an effort to reprint any foreign currency into a Frankish mold. This is not an issue in the Arab Caliphate or the Byzantine Empire. While this answers the question what currency a Frankish noble might send, it does not answer the quest of the a international currency.

Again, this applies more to the early middle ages, 700-1000 ad and around there. While you can see the use of all three currencies in Italy and in the use of Italian merchants. There is also an indication of the stability of the Arab Dinar. McCormick reveals that the Arab Dinar is used as a standard to compare other currencies to. This results from a greater political and economic stability in the Arab Caliphate during this time compare to the Byzantine and Frankish Empire. While the Frankish Empire would reprint foreign currencies, the Byzantine and other European states would take Dinars as well. Archaeological founds of coins of Dinars can be found in Italian, Byzantine, and even Slavic territories. That is in Bulgaria and Eastern European territories north of the Black Sea. The territory which is known as Kievan Rus. Which possessed an abundance of rivers that were used for trade by multiple groups, including the infamous Vikings groups that used to routes to reach the Mediterranean. This route McCormick referred to as the "Amber Trail". So seeing the Arab Dinar in so many locations and so far from Arab territories, as well as the use to compare the value of other coins in certain historical records would suggest that the Arab Dinar could be a valid international currency for the early Middle Ages.

Source: McCormick, Michael. Origins of the European Economy.Cambridge University Press. 2001