In a bowl, stir together the garlic, Worcestershire sauce, brown sugar, smoked paprika, ground coriander, 1/2 cup of the barbecue sauce, salt, and pepper until well combined.
Cut the rack of ribs in half if needed to fit into the slow cooker. Brush the ribs all over with the sauce mixture, coating evenly. Arrange them in the slow cooker and pour any remaining sauce from the bowl over the top.
Cover and cook on low for 6-7 hours or on high for 3-4 hours, until the meat is tender and begins to pull away from the bones. The internal temperature should register between 190°F and 203°F at the thickest part.
Preheat the oven to 400ºF and line a baking tray with parchment paper or foil.
Using tongs, carefully transfer the cooked ribs to the prepared baking sheet. Brush with the reserved 1/4 cup barbecue sauce.
Bake for 10 to 15 minutes, or until the sauce is thickened and caramelized on top.
Remove from the oven and let the ribs rest for 5-10 minutes before cutting into portions.
Serve warm with extra barbecue sauce on the side, if desired.