Cut the sourdough loaf in half and scoop out the bread.
In a medium saucepan over medium heat, melt the butter and mix together the scooped out bread pieces and garlic. Slowly cook and stir 10 minutes, or until the bread is browned. Transfer to a large bowl.
In the bowl with the bread mixture, mix the Monterey Jack cheese, cream cheese, Parmesan cheese and artichoke hearts. Spoon the mixture into the hollowed bread shell. Top with Cheddar cheese.
Broil 5 minutes, or until the bread is lightly brown and the cheeses are melted. Remove from oven and sprinkle with green onions. Slice and serve.