How to define a pytest fixture to be used by all tests within a given tests subdirectory?

Given a directory tests with a few subdirectories each containing test modules, how can one create a pytest fixture to be run before each test found in a particular subdirectory only?

tests
├── __init__.py
├── subdirXX
│   ├── test_module1.py
│   ├── test_module2.py
│   ├── __init__.py
├── subdirYY
│   ├── test_module3.py
│   ├── test_module4.py
│   ├── __init__.py

I'd like to have a fixture that will run before each test found in modules within the subdirYY only (in this case, in modules test_module3.py and test_module4.py).

I currently have a fixture defined twice, once inside each module within the subdirYY which works but is redundant:

@pytest.fixture(autouse=True)
def clean_directory():
   ...

If this is not possible to achieve, each of the tests within the subdirYY is decorated with a custom mark (@pytest.mark.mycustommark) so making sure that a certain fixture will run before each test marked with a particular custom mark is a viable option, too.