There is no such thing as ''a Somali maternal lineage''. Somalis have a gazillion different maternal lineages. You probably have a Somali-specific version of it nested within U3a (you need to do a full mtDNA test to reveal that, along with finding a non-related Somali U3a carrier to test along). It's probably about 5,000 years old, when MENA admixed proto-Cushites migrated from Northern Sudan (a contact zone between East Africans and North Africans/Middle Easterners).
PS. Racial purity does not exist in the strict sense, but it does exist in the loose sense of the word (as in not being admixed within the past 4,000 years).
What I mean by a Somali lineage is that my U3a is most likely a Somali specific U3a, like my E-V32. Every ethnic group in the world has a billion maternal and paternal lineages, Somalis are not special
There is Somali specific L3f, L2a1, M1a3, U6, U9, and U3a just like there is Jewish specific L2a1 and K1a
If it was present in the proto-Somalis, or stayed long enough in Somalis to be distinct from other related non-Somali lineages then it is a Somali lineage
Its redundant to be argueing for any of this baseless unprovable stuff anyways, humans dont have races, and we were mixed even before we diversified as a species to any significant degree. The entire species could have been literal half breeds even before they left the cursed continent by 100,000 years ago