In a clean jar with a tight-fitting lid, combine pomegranate juice, orange juice, mustard, honey, garlic, orange zest, and cayenne pepper. Tighten lid, and shake until everything is mixed well.
Pour over pork tenderloin in a large resealable plastic bag. Seal bag, and refrigerate for at least one hour and up to 3 hours.
Preheat oven to 350 degrees F (175 degrees C). Coat a large roasting pan with cooking spray.
Remove tenderloin from marinade, reserving the marinade.
Place meat in roasting pan, and arrange pan on center rack in oven.
Pour marinade into a small saucepan. Bring to a boil, reduce heat to simmer, and reduce volume by half.
Remove from heat.
Place 1/2 of liquid in a cup for basting, and reserve to use as a sauce.
Roast tenderloin in oven for 30 to 40 minutes, basting lightly with reduced marinade until internal temperature is 145 degrees F (63 degrees C) when measured in the thickest part of the tenderloin.
Remove tenderloin from oven, cover with foil, and let rest for 5 to 10 minutes before slicing.
Serve each portion with reserved sauce drizzled over top, and a sprinkle of pomegranate seeds.
