In a large Dutch oven, stir together the pork, wine, vinegar, bay, garlic, dried oregano, pepper flakes, cloves (if using) and 1 teaspoon each salt and pepper. Cover and refrigerate for at least 1 hour or for up to 48 hours.
When you are ready to cook the pork, heat the oven to 325°F with a rack in the lower-middle position. Set the pot, uncovered, over medium-high and bring to a simmer, stirring occasionally.
Re-cover, transfer to the oven and cook until a skewer inserted into the pork meets just a little resistance, about 1½ hours, stirring once about halfway through.
Set a wire rack in a rimmed baking sheet. Using a slotted spoon, transfer the pork and garlic to the rack, removing and discarding the bay and cloves (if used); set aside.
Tilt the pot to pool the cooking liquid to one side, then use a wide spoon to skim off as much fat as possible; reserve the fat.
Add the Madeira to the pot, bring to a boil over medium-high and cook, stirring occasionally, until the mixture has reduced to about 1 cup, 15 to 20 minutes; set aside. Remove and discard any large bits of fat on the exterior of the pieces of pork.
In a 12-inch nonstick skillet over medium-high, heat 2 tablespoons of the reserved pork fat until barely smoking. Add the pork and cook, stirring every 2 to 3 minutes, until well browned on all sides, 5 to 7 minutes.
Remove the skillet from the heat and add the reduced cooking liquid. Return to medium-high and continue to cook, stirring occasionally, until the liquid has reduced and the pork is lightly glazed and begins to sizzle, 3 to 5 minutes.
Taste and season with salt and black pepper, then stir in the fresh oregano. Transfer to a serving dish.