The first Vernal Equinox recorded in Rig Veda is that of star Ashwini, which is reported to have occurred around 10,000 BC. Subash Kak, a Computer Engineer and reputed Indologist, decoded the RigVeda and found many astronomical concepts therein.
This is clearly an indication of the fact that the Hinduism is at least 10,000 BC old as Rig Vedas are the first books on hindu thought
This is how far Hinduism had spread at its greatest territorial extent
All of the Indian subcontinent was already in the sway of Hindu culture.
Also note, Vedic culture and Buddhist beliefs had penetrated as far as Afghanistan and beyond, Ancient Iran had a cultural tradition very similar to Vedic Hinduism (even sharing many of the same Gods) and similar rituals, for example worship using fire altars and the like. People from such dispaarate ethnic backgrounds as the Scythians of central Asia and the Yeuzhi (the Kushans) of the Chinese mainland and the Greeks (Yavanas) have appropriated Hindu ideals and customs.
So saying that Hinduism is a domestic religion is grossly inaccurate statement, many of these regions still practice Hindu customs and rituals, which have cross-pollinated with local culture to create some stunningly beautiful imagery.
This is from Bali, Indonesia
And here is Lord Ram…..from Thailand
The largest religious monument in existence, also happens to be the largest Hindu temple complex known, dedicated to Vishnu, it is situated in Cambodia, hundreds of miles from the Indian mainland