Hinduism
Hinduism has been too diverse to be seen as a monolithic religion, and with a conspicuous absence of any listed dogma or ecclesia (organised church), has no concept of excommunication and hence no Hindu may be ousted from the Hindu religion, although a person may easily lose caste status for a very wide variety of infringements of caste prohibitions. This may or may not be recoverable. However, some of the modern organized sects within Hinduism may practice something equivalent to excommunication today, by ousting a person from their own sect.
In medieval and early-modern times (and sometimes even now) in South Asia, excommunication from one's caste (jati or varna) used to be practiced (by the caste-councils) and was often with serious consequences, such as abasement of the person's caste status and even throwing him into the sphere of the untouchables or bhangi. In the 19th century, a Hindu faced excommunication for going abroad, since it was presumed he would be forced to break caste restrictions and, as a result, become polluted.
After excommunication, it would depend upon the caste-council whether they would accept any form of repentance (ritual or otherwise) or not. Such current examples of excommunication in Hinduism are often more political or social rather than religious, for example the excommunication of lower castes for refusing to work as scavengers in Tamil Nadu.
An earlier example of excommunication in Hinduism is that of Shastri Yagnapurushdas, who voluntarily left and was later expelled from the Vadtal Gadi of the Swaminarayan Sampraday by the then Vadtal acharya in 1906. He went on to form his own institution, Bochasanwasi Swaminarayan Sanstha or BSS (now BAPS) claiming Gunatitanand Swami was the rightful spiritual successor to Swaminarayan.
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