from typing import List
from typing import Dict


def get_source2target_domain_mapping(source_domains: List[str], target_domains: List[str]) -> Dict[str, List[str]]:
    """Helper function to return cross domains keys for each domains.

    Args:
        source_domains (List[str]): list of all source domains
        target_domains (List[str]): list of all target domains

    Returns:
        Dict[str, List[str]]: return a list of cross domains per domain keys.
    """
    mapping = {}
    for dom in source_domains:
        mapping[dom] = [d for d in target_domains if d != dom]
    return mapping