Pour the water into a 2-cup glass measuring cup, add the porcinis, and stir to submerge. Cover with a plate. Let soak until the mushrooms are soft, 20 to 30 minutes. Drain, reserving 1 cup of the soaking liquid and the porcini separately. If the porcini pieces are large, roughly chop them and set aside.
While the mushrooms are soaking, prepare the pork chops. In a small bowl combine 2 teaspoons of the rosemary, 1 teaspoon salt, and ½ teaspoon pepper. Brush the pork chops on both sides with the oil and season evenly with the spices.
Prepare the grill for direct cooking over high heat (450° to 550°F).
In a large skillet over medium-high heat, melt the butter. Add the creminis and cook until they release their liquid and become tender and browned, 7 to 8 minutes, stirring frequently. Stir in the drained porcini, ¾ cup of the scallions, and the remaining 1¼ teaspoons rosemary. Sauté for 2 minutes. Add the marsala and boil until reduced by about half, 1 to 2 minutes. Add the broth and the 1 cup reserved porcini soaking liquid, leaving any sediment behind. Boil until slightly reduced, 3 to 4 minutes. Stir in the cream and boil until the liquid thickens to your desired sauce consistency, 3 to 5 minutes. Season the sauce with ½ teaspoon salt and ¼ teaspoon pepper.
Brush the cooking grates clean. Grill the pork chops over direct high heat, with the lid closed as much as possible, until they are still slightly pink in the center, 6 to 8 minutes, turning once or twice. Remove from the grill and let rest for 3 to 5 minutes. Spoon the mushroom sauce over the pork chops and top with the remaining ¼ cup scallions. Serve warm.