Stir together the flour, 1 teaspoon salt, pepper and cumin in a large bowl. Place the cubed pork into the mixture and stir well to coat the meat with the seasonings.
Heat the olive oil in a large heavy pan over medium-high heat until the oil shimmers. Working in batches if necessary, place the meat into the hot pan in a single layer. Pan-fry the pork until brown on all sides, about 15 minutes. Remove the pork to a bowl and cover to keep warm.
Cook and stir the onion in the hot pan over medium heat, adding more olive oil if necessary, until the onion is translucent and beginning to brown, about 7 minutes.
Return the meat to the pan and stir in the garlic, tomatillos, chillies, marjoram, coriander and water. Check seasoning and add 1 pinch of salt to taste, if needed. Cover and simmer over low heat, stirring occasionally, until the meat is tender, about 1 hour.
Skim excess fat off the stew before serving in bowls, garnished with a dollop of sour cream and a coriander sprig on each bowl.