Clean sweeps of Test series of 3,4 and 5 matches are not as rare as one may think. Here is Cricinfo’s listing:
India has recorded clean sweeps at home earlier (and have faced 5-0 sweeps against England and the West Indies as well, but never at home). India had already won against England 3-0 in 1992-93, against Sri Lanka 3-0 (all by an innings) in 1993-94, against Australia 4-0 in 2012-2013, against New Zealand 3-0 in 2016-17 and now 3-0 against Sri Lanka in Sri Lanka.
This is not, however, the first time India have won 3 Tests in an away series. They defeated New Zealand 3-1 in 1967-68, achieving India’s first Test and series win outside India. This series is often forgotten, probably because of New Zealand’s low standing at that time and also because India had just endured a 3-0 loss in England followed by a 4-0 loss in Australia.
There were also mini-sweeps (2-0) by India in Bangladesh (2004-05 and 2009-10), in Zimbabwe (2005-06) and in the West Indies (2019). Similarly India lost 2-0 to South Africa at home in 1999-2000.
The current series included wins by 304 runs followed by two innings wins (though the first Test was effectively an innings defeat as the total of Sri Lanka’s two innings was less than India’s first innings total). Again, this is not new as India had won all 3 Tests by an innings at home against the same opposition in 1993-94. Other examples of this kind include the West Indies losing all 3 Tests by an innings in their first series against England in 1928.
West Indies is the only team to win 4-0 or 5-0 away. They won 5-0 against England in England in 1984, and followed this with 5-0 at home in 1985-86 against the same opponents.
There was a tinge of black humor in reportage of these West Indies victories in the 1980s. Earlier the term “whitewash” was commonly used for a clean sweep, so it was but natural that a 5-0 victory by the West Indies would be called a “blackwash”, as in 1984 and 1985-86. By 1988 England had improved a bit and lost the 5-Test home series 4-0. This was dubbed a “dark grey wash”.
Then there was India’s “brownwash” of England in 1992-93.
3-0 sweeps away from home are not too common. They are:
Eng in NZ, 1962-63
Aus in NZ, 1999-2000
Aus in SL, 2003-04
Aus in SA, 2005-06
Ind in SL, 2017
Eng in SL, 2018-2019
And in neutral venues:
Aus v Pak, 2002-03
Pak v Eng, 2011-12.
There have been many near-clean sweeps of 4-0 and 4-1 in 5-Test series. In the 6-Test series which were played between the 1970s and 1990s, we have two examples of 5-1 margins:
Aus v WI in Aus, 1975-76
Eng v Aus in Aus, 1978-79