malechh actually referred to a tribe from a country neighbouring Indiasomewhere around Nepal if i remember correctly  who did not follow the sanatan dharm old name of Hinduism The came to be used for nonhindus and nonsikhs though not necessarily as a derogatory term  It however does crop up in the litterature of Hindu Right Wing Sangh Parivar as generic term for NonHindus And of course you will also find in antiindian antihindu sites too     google for more proof